1. Field of the Invention
The present invention relates to a one-step process for the preparation of alkyl glycosides and alkyl polyglycosides by acid-catalyzed reaction of saccharides with alcohols having 12 to 20 C atoms.
2. Description of the Background
Alkyl glycosides and alkyl polyglycosides having C.sub.12 - to C.sub.20 -alkyl radicals can be prepared completely or partially from renewable raw materials. These alkyl glycosides and alkyl polyglycosides are obtaining increasing importance because of their interesting surfactant properties and at the same time their very good biological degradability. For applications in the household and in the cosmetics field, these products must satisfy high aesthetic demands. There is therefore an interest in processes by which alkyl glycosides and alkyl polyglycosides can be prepared in transparent aqueous solutions of good color.
In order to prepare alkyl glycosides and alkyl polyglycosides having long-chain alkyl groups, it is possible initially to prepare alkyl glycosides and alkyl polyglycosides having C.sub.1 - to C.sub.6 -alkyl groups by glycosylation of saccharides with short-chain alcohols. These products are then converted into the desired alkyl glycosides and alkyl polyglycosides using long-chain alcohols by trans-glycosylation at elevated temperature. However, the products prepared in this way are dark-colored.
According to EP 0,165,721, the color of products of this type can be improved by multi-step bleaching with hydrogen peroxide and stabilized by the addition of compounds releasing sulfur dioxide. The brightening effect is only of short duration without sulfur dioxide.
EP 0,077,167 describes a one-step preparation process in which an aldose or a ketose is reacted directly with a long-chain alcohol in a molar ratio of 1:1.25 to 1:4. The reaction is carried out at low water contents in the presence of a reducing agent. The reducing agent used is chiefly hypophosphorous acid. The sodium hypophosphite likewise employed is used in amounts of less than 0.4%, relative to the saccharide. After the reaction, the product is neutralized with alkali, after which excess long-chain alcohol is removed by distillation. It has been found that this process leads to distinctly colored products when using alcohols having 12 to 20 C atoms and a need thereby exists for a method of decoloring alkyl glycosides and alkyl polyglycosides.